(1) Technical Field
The present invention relates to electronic pulse dialers as utilized in connection with telephones and more particularly to pulse dialers employing current regulators.
(2) Background Art
Pulse dialers have been used in telephones to provide pushbutton operation while retaining conventional dial pulse signalling. To provide this feature, a pulse dialer is typically connected across the telephone loop and operates to provide pulse signals by breaking and closing the loop. However, since the pulse dialer is connected across the loop it typically presents a low impedance during transmission or open circuit pulsing conditions. Since a true open loop condition does not exist during the break period of out pulsing, dial pulse distortion (low amplitude pulses) frequently results causing a reduction in the usable loop length of the telephone line. Similarly, the pulse dialer presents a low impedance across the loop during transmission conditions, thus shunting these signals and causing a resulting degradation of transmission characteristics. These problems are typically inherent in electronic pulse dialers and have been overcome through the use of relays to break the loop and provide true open circuit conditions.
A technique for overcoming the above objections is provided in my U.S. Pat. No. 4,286,120 issued on Aug. 25, 1981, wherein a high impedance is presented across the telephone line during transmission and interpulse pause conditions by the incorporation of a current source to supply current to the pulse dialer during the "OFF HOOK" condition.
Integrated dialing circuits (both dual tone multi frequency and pulse) have been used in the design of telephones recently. Some of the circuits available as integrated units, have the ability to store one or more telephone numbers which may then be automatically dialed upon command usually by operating a command pushbutton followed by a single digit pushbutton. In order to maintain the information relating to the stored telephone numbers, in memory, voltage must be maintained on the integrated circuit continuously. To this end, several methods have been employed. Among these are the use of an external battery and voltage obtained from the telephone loop itself. The use of external batteries carries with it the disadvantage of being expensive and requiring periodic replacement. Alternatively, powering the integrated circuit from the telephone loop has the disadvantage that the amount of current drawn by the integrated circuit for memory retention during the time the telephone is "ON HOOK" must be very small (usually less than 5 microamps). The most common technique employed previously to limit current in the "ON HOOK" condition has been to connect the integrated circuit to the loop via a large value resistor (5 to 10 megohms typically). The resistor method however has the disadvantage that the current and voltage supplied to the integrated circuit is not constant under all loop conditions presented to the telephone. For example, long telephone loops, low central office batteries and telephones in parallel on the same loop, act to reduce the voltage and current available to retain the stored information in memory. Such conditions typically result in failure of existing telephone circuitry to retain the desired information in memory.
Accordingly, it is the object of the present invention to provide a novel low cost and highly reliable means of providing open circuit conditions to a telephone during transmission and interpulse pause conditions and to provide regulated current to an included integrated circuit dialer (which includes a memory with the ability to store one or more telephone numbers), with a regulated source of current during the "ON HOOK" condition.